Process for desulfurization with regenerable salts of weak acids



United States Patent 0 3,380,915 PROCESS FOR DESULFURIZATION WITHREGENERABLE SALTS 0F WEAK ACIDS William J. Mattox and William F. Arey,Jr., Baton Rouge,

La., assignors to Esso Research and Engineering Company, a corporationof Delaware No Drawing. Filed Sept. 29, 1965, Ser. No. 491,381 4 Claims.(Cl. 208-284) ABSTRACT OF THE DISCLOSURE Petroleum residua aredesulfurized by contacting with a treating agent comprisin an alkalimetal salt of a weak, nonvolatile acid. Alkali metal salts which may beemployed for this purpose include the aluminates, antimonates,arsenates, arsenites, molybdates, stannates, silicates, tungstates,vanadates, etc. The salts are regenerable from the spent reagent byfusion of the alkali metal carbonate and alkali metal sulfide thereinwith the oxide corresponding to the acid anion of said weak acids.

This invention relates to a process for the removal of sulfur fromliquid hydrocarbon streams, particularly petroleum residua. Morespecifically, the invention relates to the desulfurization of petroleumresidua with certain regenerable salts of weak acids.

Generally, sulfur occurs in petroleum stocks in one of the followingforms: mercaptans, sulfides, disulfides, and as part of a more or lesssubstituted ring, of which thiophene, benzothiophene, anddibenzothiophene are the prototypes. The mercaptans are generally foundin the lower boiling fractions, e.g., naptha, kerosene, and light gasoil. Numerous processes for sulfur removal from these lower boilingfractions have been suggested, such as doctor" sweetening (whereinmercaptans are converted to disulfides), caustic treating, solventextraction, copper chloride treating, and so forth, all of which give amore or less satisfactory decrease in sulfur or in deactivation ofmercaptans by their conversion into disulfides. When the process resultsin the latter effect, the disulfides generally remain in the treatedproduct and must be removed by another step if it is desired to obtain asulfur-free product.

Sulfur removal from higher boiling fractions, however, has been a muchmore difiicult operation. Here, the sulfur is present for the most partin the less reactive forms as sulfides, disulfides, and as a part of aring compound, such as substituted thiophenes. Said sulfur, of course,is not susceptible to chemical operations satisfactory for removal ofmercaptans. Extraction processes employing sulfur-selective solvents arealso unsatisfactory because the high boiling fractions contain a muchhigher percentage of sulfur-containing molecules; for example, even if aresiduum contains only about 3% sulfur, it is estimated thatsubstantially all the molecules may contain sulfur. Thus, if such aresiduum were extracted with a solvent selective to sulfur compounds,the bulk of the residuum would be extracted and lost.

A process for the chemical desulfurization of residuum stocks employingfused alkali metal hydroxides has been disclosed by Mattox in US. Patent3,164,545, issued January 5, 1965. While contaminant removal isexcellent using fused alkali metal hydroxides, the process suffers fromthe inherent defect that the treating agent becomes spent and it must beregenerated in a multi-step regeneration sequence.

The object of this invention is to provide a process for thedesulfurization of residuum in which regeneration can be achieved by asingle regeneration step in a simple and straightforward manner. We havefound that certain regenerable salts of weak acids are effectivechemical desulfurization reagents.

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The invention will be further illustrated by the following descriptionand examples.

Generally speaking, the process involves contacting the oil at elevatedtemperature with an alkali metal salt of a weak acid and regeneratingthe sulfide, hydrosulfide and/ or carbonate of the alkali metal formedin the desulfurization step by fusion with the corresponding metal oxideor in some instances by slurrying the oxide in an aqueous solution ofthe carbonate and/or the sulfide.

The desulfurization feedstock comprises a heavy hydrocarbon oilcontaining an appreciable quantity of sulfur compounds, i.e., from about0.5 to 10.0 Wt. percent sulfur. Specific examples include heavy wholecrude oils, topped crude oils, deasphalted oils, atmospheric residua,shale oils, and the like. Petroleum residua having an initial boilingpoint above about 600 F. are preferred feeds.

The petroleum residuum is contacted in any suitable reaction vessel,preferably a vessel lined with a corrosion resistant material. Reactionconditions include temperatures ranging from 300-1000" F., preferablySOD-800 F. Sub-atmospheric pressures can be used but elevated pressures,i.e., 142000 p.s.i., are preferred. The quantity of salt will range from10-200 wt. percent based on the oil feed. Contacting times range up to20 hours. Continuous or batch contacting can be used.

The amount of water associated with the salt is important. The watercontent should be within the range of from about 3-30 wt. percent basedon the salt.

A large number of alkali metal salts of weak, nonvolatile acids areavailable and are suitable for use in this process. By weak, nonvolatileacids we mean acids (1) having acidities approximately the same or lessthan carbonic acid and (2) being of a nature wherein the oxide orsulfide corresponding to the acid anion is not gaseous at temperaturesbelow 1000 F. The following salts are illustrative: aluminates ('KALOantimonates (KSbO KSbO K Sb O KH(SbO K H Sb O KSb(OH) arsenates andarsenites (K AsO KAsO KH AsO KAsO K AsO KAsO -HAsO manganate (K MnOmolybdates (K MoO osmates (K OsO plumbates (KgPbOg, 6) silicates(K4Si04, K2SiO K Si O stannates (K 'SnO K Sn(OH) tellurates andtellurites (K TeO K TeO tungstates (K WO uranates (K UO K U O vanadates(KVO etc.

The reaction may be improved by passing air or oxygen into the reactorduring the desulfurization or by preoxidizing the petroleum feedstock.Air rates of l-l500 standard cubic feet per barrel can be used. If thefeedstock is preoxidized, contacting temperatures ranging from 200-800F. and contacting times ranging from 10 minutes to 10 hours aresuitable.

The alkali metal salts of weak nonvolatile acids are readily preparedfrom the carbonates or the sulfides of the particular alkali metalinvolved and the appropriate metal oxide or silica by fusion at about700-1200" F. or, in some instances, such as with the molybdates, merelyby contacting an aqueous slurry. The preparation of potassium silicateis shown by the following formula:

KgS+KzCO3+2slOg+Hg0 2KzSiO +COz+HzS Desulfurization with potassiumsilicate can be illustrated by the following reactions at 600650 F.:

(2) KOI-I-H-ligh S Oil Feed- Low S Oil Potassium silicate, potassiumstannate, potassium molybdate, potassium meta-antimonate, and potassiumaluminate have shown about 2030% sulfur removal from West Texasdeasphalted oil at 600650 F. The following tabulation shows the resultsof the desulfurization with a selected group of alkali metal salts ofweak acids.

TABLE I.-DESULFURIZATION OF WEST TEXAS DEAS- generfted by carrying out hfollowlng feflctlof} a PHALTED OIL WITH ALKALI METAL SALTS; FOUR-HOUR1200 F. and pressures ranging from 1-20() p.s.1.a. TREATS; GOO-650 F.;0.5-1.1 SALT/OIL WT. RATIOS K S K CO 250 2K S C0 +H S 1 1 Percent P tgerlgent Diasutlai. 2 2 3+ 2 2 3+ 2 2 d Water on Pressure wi Similaralkali metal salts of weak acids can be re enerate D lf. Amount of vsalt Reagent p s 1 g Fused KOH, by the same method. Certam salts such asthe molybdates Cmemed Data can be regenerated by contacting in anaqueous slurry, as 100 397 22 21 follows:

3 3 5g M0O +H O+H MoO 1 1% hi 22 H2M r+1 2 3+K2M 4+H2 2 i3 $2 Theforegoing description and examples clearly show 18 12 the advantages ofalkali metal salts of Weak non-volatile 20 55 2s 3s so 430 23 acids fordesulfurrzation of heavy 011s.

What is claimed is:

Data obtained in these tests, particularly with the sili- 15 1 Thprocess f removing lf r im uritie from Cate and meta-flntimonaiel Showthe necessity {0r adding petroleum residua containing 0.5 to 10.0 wt.percent sul- PP P quantities of Water' These amounts Presently fur andhaving an initial boiling point above about 600 pp to 13$ Within the ofabout Percent F. which comprises continuously contacting the residuabased on the Weight of th@ Salt used and y With the at a temperature inthe range of 500800 F. with a treatsalt. Summarized effects of waterratios on desulfuriza- 2O i agent comprising an lk li t l lt f a e k,ontion with the silicate and mcta-antim nat ar h Wn volatile acid havingan acidity equal to or less than carbelow. bonic acid and 3-30 wt.percent water based on the salt TABLE II.DESULFURIZATION OF PREOXIDIZEDWEST and recovering desulful'iled Petroleum residua- TEXAS OIL 'ITHK-SILICATE AND 71TH Ksboa; 4-HOUR 2 The -process of claim 1 whe gin thefeed is peroxi- TREATS dized prior to said contacting.

Weight Water Ratio 3. The process of claim 1 wherein the alkali metalsalt Percent Percent Esau Sm Weight M015] n 1s selected from the groupconsistlng of potassium silicate 011 Oil 15 1 1 15 MoIK Iizfliionpotassium stannate, potassium molybdate, potassium meta-antimonate andpotassium aluminate. Antimonm 98 0 0 4. The process of removing sulfurimpurities from peg3 18 21 20 troleum resldua containing 0.5 to 10.0 wt.percent sulfur 3g 8 8' i3 and having an initiakboiling point above about600 F. 100 15 Q9 22 which comprises continuously contacting the residuaat a 100 30 L8 11 temperature in the range of 300 to 1000 F., with atreat- 111g agent comprising an alkali metal salt of a weak, nonvolatileacid having an acidity equal to or less than carbonic acid andcontaining 3-30 wt. percent water based onthe total reagent, separatingdesulfurized oil from TABLE III-DESULFURIZATI0N OF WEST TEXAS spentreagent, regenerating said spent reagent comprising It has also beenascertained that multi-stage treatments optimize conversion and thebeneficial effects are shown below:

ASPHALTED OIL WITH KSbO V1 670 F.

v a 3 alkali metal carbonate and alkall metal sulfide by fuslon N0.ofStages 1n treat 1 1 1 2 with the oxide corresponding to the acid anionof said Percent KSbO; on Oil, total 49 98 195 200 acid nd p s ing theregenerated reagent to the contacting Percent Desulfurization a. 15 303331 44 Zone Oxygen promotion has a very pronounced eifect on 1-References Clted desulfurization with these salts, as illustrated withpotas- 0 UNITED STATES PATENTS sium antimonate. 1,540,218 6/1925 Maloney208285 TABLE IV,-EFFECTS or OXYGEN PROMOTION ON K-SALT 1,927,182 9/1933Morreu 208191 QESULFURIZATION: 650 1 44101111 TREATS; 1 1 RATIO1,942,054 1/1934 Garrison 208 226 kSbOH/W- TEXAS OIL 50 2,124,314 7/1938Stagni 20s 2s4 Feed Pretreat Percent H2O Percent S 2,434,868 1/ 1948Sample et al 208230 B03681 Removal 2,944,016 7/1960 Thomas 208 2s4 N0ne.3 10 3,152,070 10/1964 Lehman et a1. 208-285 Pl'ewdlzed 3 M3 3,164,5451/1965 Mattox 2os 23o As the desulfurization reaction proceeds thetreating agent becomes Spent and K28 and Kzcos are formed DELBERT E.GANTZ, Plzmary Examine). when the potassium salt is used. Potassiumsilicate is re- G. J. CRASANAKIS, Assistant Examiner.

